The present invention relates to a method of increasing heat transfer of a fitted material of a cylinder head in an internal combustion engine and a fitted portion of the fitted material for which the method is carried out.
An exhaust bore of a cylinder head in an internal combustion engine is periodically opened and closed by a valve which moves up and down by a rocker arm and a coil spring.
A valve stem is slidably inserted in a tubular valve guide above an inlet of the exhaust hole. With moving up and down, a valve face of a valve head at the lower end of the valve is engaged on and disengaged from a valve seat fixed on the inlet of the exhaust hole.
The valve guide and the valve seat require high heat, wear and impact resistance, are made of heat resistant steel different from material of the cylinder head such as cast iron and light metal, and are strongly fixed in the exhaust hole of the cylinder head.
The valve guide and the valve seat called "fitted material" are highly finished and firmly engaged to fit on each of the inner surfaces of the exhaust hole of the cylinder head. But the fitted material and the exhaust hole are not thermally integral.
Even if finishing accuracy of the contacting surfaces is increased and even if strong and complete fitness is mechanically made, it is unavoidable to remain fine unevenness. Gaps in the unevenness cause level difference in heat transfer in the contacting surfaces, thereby making it insufficient to transfer heat of the fitted material to the cylinder head.
If the fitted material and the cylinder head are formed to thermally or metallurgically integral material, heat transfer of the fitted material will be clearly improved, thereby increasing durability of the fitted material and the cooling effect of the whole cylinder head.
It is an object of the present invention to provide a method of melting soldering material during initial operation of an internal combustion engine or heating at a desired temperature, but not melting thereafter, and to provide a fitted portion of fitted material.